import java.util.*;

public class BST<E extends Comparable<E>> {

    private class Node{
        public E e;
        public Node left;
        public Node right;

        public Node(E e){
            this.e = e;
            left = null;
            right = null;
        }
    }

    private Node root;
    private int size;

    public BST(){
        root = null;
        size = 0;
    }

    public int getSize(){
        return size;
    }

    public boolean isEmpty(){
        return size == 0;
    }

    //向二分搜索树添加元素e
    public void add(E e){
        root = add(root,e);
    }
    //添加元素的递归算法，向以node为根的二分搜索树插入元素e
    //返回插入新节点后二叉搜索树的根
    private Node add(Node node,E e){
        if(node == null){
            size++;
            return new Node(e);
        }
        if(e.compareTo(node.e) < 0){
            node.left = add(node.left,e);
        }else if(e.compareTo(node.e) > 0){
            node.right = add(node.right,e);
        }
        return node;
    }

    //查看二分搜索树中是否存在元素e
    public boolean contains(E e){
        return contains(root,e);
    }
    //以node为根的二分搜索树是否存在元素e，递归算法
    private boolean contains(Node node,E e){
        if(node == null){
            return false;
        }else {
            if(e.equals(node.e)){
                return true;
            }else if(e.compareTo(node.e) < 0){
                return contains(node.left,e);
            }else {
                return contains(node.right,e);
            }
        }
    }

    //寻找二分搜索树的最小元素
    public E minimum(){
        if(size == 0){
            throw new IllegalArgumentException("BST is empty!");
        }
        return minimum(root).e;
    }
    //返回以node为根的二分搜索树的最小值所在的结点
    private Node minimum(Node node){
        if(node.left == null){
            return node;
        }
        return minimum(node.left);
    }

    //寻找二分搜索树的最大元素
    public E maximum(){
        if(size == 0){
            throw new IllegalArgumentException("BST is empty!");
        }
        return maximum(root).e;
    }
    //返回以node为根的二分搜索树的最大值所在的结点
    private Node maximum(Node node){
        if(node.right == null){
            return node;
        }
        return maximum(node.right);
    }

    //二分搜索树删除最小值
    public E removeMin(){
        E ret = minimum();
        removeMin(root);
        return ret;
    }
    //删除以node为根的二分搜索树的最小值所在的结点
    //返回删除结点后二叉搜索树的根
    private Node removeMin(Node node){
        if(node.left == null){
            Node rightNode = node.right;
            node.right = null;
            size--;
            return rightNode;
        }
        node.left = removeMin(node.left);
        return node;
    }

    //二分搜索树删除最大值
    public E removeMax(){
        E ret = maximum();
        removeMax(root);
        return ret;
    }
    //删除以node为根的二分搜索树的最大值所在的结点
    //返回删除结点后二叉搜索树的根
    private Node removeMax(Node node){
        if(node.right == null){
            Node leftNode = node.left;
            node.left = null;
            size--;
            return leftNode;
        }
        node.right = removeMax(node.right);
        return node;
    }

    //删除二分搜索树的任意元素
    public void remove(E e){
        root = remove(root,e);
    }
    //删除以node为根的二分搜索树的值为e所在的结点
    //返回删除结点后二叉搜索树的根
    private Node remove(Node node,E e){
         if(node == null){
             return null;
         }
         if(e.compareTo(node.e) < 0){
             node.left = remove(node.left,e);
             return node;
         }else if(e.compareTo(node.e) > 0){
             node.right = remove(node.right,e);
             return node;
         }else{
             //左子树为空
             if(node.left == null){
                 Node rightNode = node.right;
                 node.right = null;
                 size--;
                 return rightNode;
             }
             //右子树为空
             if(node.right == null){
                 Node leftNode = node.left;
                 node.left = null;
                 size--;
                 return leftNode;
             }
             //左右子树都不为空
             //找到比待删除节点大的最小节点，即待删除节点右子树的最小节点
             //用这个节点顶替待删除节点的位置
             Node successor = minimum(node.right);
             successor.right = removeMin(node.right);
             successor.left = node.left;

             node.left = node.right = null;

             return successor;
         }
    }

    //二分搜索树的前序遍历
    public void preOrder(){
        preOrder(root);
    }
    //前序遍历以node为根的二叉搜索树，递归算法
    private void preOrder(Node node){
        if(node != null){
            System.out.println(node.e);
            preOrder(node.left);
            preOrder(node.right);
        }
    }
    //前序遍历的非递归算法
    public void preOrderNR(){
        Stack<Node> stack = new Stack<>();
        stack.push(root);
        while (!stack.isEmpty()){
            Node cur = stack.pop();
            System.out.println(cur.e);
            if(cur.right != null){
                stack.push(cur.right);
            }
            if(cur.left != null){
                stack.push(cur.left);
            }
        }
    }

    //二分搜索树的中序遍历，应用于排序
    public void inOrder(){
        inOrder(root);
    }
    //中序遍历以node为根的二叉搜索树，递归算法
    private void inOrder(Node node){
        if(node != null){
            inOrder(node.left);
            System.out.println(node.e);
            inOrder(node.right);
        }
    }

    //二分搜索树的后序遍历,应用于释放内存
    public void postOrder(){
        postOrder(root);
    }
    //后序遍历以node为根的二叉搜索树，递归算法
    private void postOrder(Node node){
        if (node != null){
            postOrder(node.left);
            postOrder(node.right);
            System.out.println(node.e);
        }
    }

    //层序遍历,可以更快找到元素。
    public void levelOrder(){
        Queue<Node> q = new LinkedList<>();
        q.add(root);
        while (!q.isEmpty()){
            Node cur = q.remove();
            System.out.println(cur.e);

            if(cur.left != null){
                q.add(cur.left);
            }
            if(cur.right != null){
                q.add(cur.right);
            }
        }

    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        generateBSTString(root,0,res);
        return res.toString();
    }
    //生成以node为根节点，深度为depth的描述二叉树的字符串
    private void generateBSTString(Node node,int depth,StringBuilder res){
        if(node == null){
            res.append(generateDepthString(depth) + "null\n");
            return;
        }
        res.append(generateDepthString(depth) + node.e + "\n");
        generateBSTString(node.left,depth+1,res);
        generateBSTString(node.right,depth+1,res);
    }

    private String generateDepthString(int depth){
        StringBuilder res = new StringBuilder();
        for (int i = 0; i < depth; i++) {
            res.append("--");
        }
        return res.toString();
    }

}
